Pressure sealing of plated envelope sections



y 1965 R. D. CULBERTSON ETAL 3,193,920

PRESSURE SEALING OF PLATED ENVELOPE SECTIONS Ongmal Flled Aug 17, 1959 ZZIZ ZZZZI INVENTORS. ROBERT D. CULBERTSON RUSSELL c. McRAE Y c. WARNER ATTORNEYS United States Patent 3,193,920 PRESSURE SEALIN G 01 PLATED ENVELOIE SECTIQNS Robert D. Culbertson, San Jose, Russell C. McRae, Santa Clara, and Harvey C. Warner, Belmont, Califi, assignors to Eitel-McCullongh, Inc, San Carlos, CaliL, a corporation of California Original application Aug. 17, 1959, Ser. No. 834,219. Divided and this application Nov. 13, 1962, Ser. No. 237,208

4 Claims. (Cl. 29492) This application is a division of our copending application Serial No. 834,219, filed August 17, 1959.

This invention relates to an electron tube and more particularly to an electron tube having a pressure seal and to a method of and a means for making such a seal. The term pressure seal is defined for use herein as a permanent vacuum-tight seal obtained by the application of pressure at temperature below the melting point of any of the materials in the seal.

With the introduction of high alumina ceramic electron tubes, various types of pressure seals were developed to seal ceramic to ceramic or ceramic to metal.

None of these types of seals are effective in sealing two parts of [a miniature electron tube, especially when the tube dimensions are in the order of one-half inch long and one-quarter inch in diameter. In pressure sealing a miniature diode that requires at least three electrical leads and is limited to two ceramic ring insulators, the electrical lead, which is in the form of a ring and positioned between the two ceramics, is required to be made of hard metal such as Kovar so that it will not deform under sealing pressure destroying the metal to ceramic bond, as Well as making it .difiicult to obtain accurate electrical spacing. The art of pressure welding two pieces of metal teaches that hard metals require larger pressures for pressure welding than softer metals. The pressure required to weld Kovar is too high and not practical in the fabrication of a miniature tube.

In this application Kovar refers to metal alloys comprising primarily iron, nickel and cobalt with some manganese and having a coefiicient of thermal expansion approximately 5X .per degree Centigrade.

It is an object of the present invention to provide an electron tube with a pressure seal between two pieces of hard metals.

It is another object of the present invention to provide a pressure sealing method between hard metal surfaces which do not require optical flat joining surfaces.

It is yet another object of the present invention to provide a pressure seal, a method of and a means for making such seal between hard metal rings in an electron tube.

In one embodiment the invention involves making hard metal pressure seals for electron tubes by plating the hard metal sealing rings with a soft ductile metal. A soft ductile metal sealing gasket placed between the two soft met-a1 clad surfaces on each of the hard metal rings. Force is applied to the hard metal rings until the gasket yields and deforms. In so doing the gasket adheres to the plated surfaces.

The invention possesses other objects and features of advantage, some of which, with the foregoing, will be set forth in the following description of the invention. It is to be understood that the invention is not limited to the disclosed species, as variant embodiments there- :of are contemplated and may be adopted Within the scope of the claims.

Referring to the drawings:

FIGURE 1 is a sectional elevation of a typical die press fixture, through which pressure is applied to the sealing rim of an electron tube.

3,193,920 Patented July 13, 1935 FIGURE 2 is an enlarged view of the sealing rim of an electron tube before pressure is applied.

FIGURE 3 is a sectional elevation of the sealed electron tube.

Refer-ring now to the drawings and to FIGURE 1 in particular, there is shown an electron tube in two sections which are to be sealed together. The two sections are cathode section 12 and an anode section 14. The cathode section 12 is suspended within an axial well 16 formed in a ram 18. The ram 18 and a die 20 form a die press fixture. The cathode section is held by a wire 22 which is suspended through an aperture 24 in the ram 18. The end of thewire 22 within the well 16 is fixed to a sealing means 26 which is a metallic plate joined to a ceramic cylinder 28 of the cathode section 12 by means of a conventional ceramic-to-metal bond. Wire 22 may be fixed to sealing means 26 with soft solder. The wire is then passed through aperture 24 and the cathode section is drawn up tight against the ram 18. The wires free end protruding from the ram is bent to hold the cathode section in place. other end :of the ceramic cylinder 28 is bonded a terminal sealing ring 30 preferably made of Kovar. terminal sealing ring 30' is plated with a soft, highly ductile metal 32 such as oxygen-free, high conductivity copper, which in this embodiment is plated on both sides of the Kovar, as shown, although it is actually necessary to plate only the side of the Kovar to be pressure sealed. The plating is preferably between .001 and .002 inch thick and the ring 30 is about .010 inch thick. A

' cathode 33 with an emitting surface 34 coplanar with the plated 32 surface of the terminal ring 30 is mounted thereto.

The anode section 14 is similar to the cathodesection in that sealing means 26' formed into a cup-shaped metal section is sealed to a similar ceramic cylinder 28' and a terminal ring 30' is joined to the other end of the ceramic cylinder 28' by means of a conventional ceramic-to-metal bond. Ring 30' is also made of a hard met-a1 such as Kovar. The sealing means 26' is the anode with a face 35 coplanar with the plated 32' surface of the terminal sealing ring 30'. Similarly to ring 30, the ring 30 is also copper plated as represented by plated layers 32'. The anode section 14 fits into the die 20 with the ceramic section 28' disposed within a bore 34 of the die 20 and the terminal sealing ring 30' bearing on a shoulder formed by a larger bore' 36 into which is disposed the ram 18.

The pressure seal is formed between the two rings 30 and 30' by first cleaning the sealing surfaces which are the copper plated surfaces 32 and 32 which face each. other and cleaning a soft highly ductile metallic seal ing gasket 38 made of the same material as the plated surfaces 32 and 32', and in this embodiment being oxygen free, high conductivity copper, all being cleaned with a standard acid process. The two sections 12 and 14 and the copper gasket 38 are afterward wet-hydrogen fired at approximately 800 C. to anneal, degas and remove carbon residue. The two sections 12 and 14 are assembled to the ram 18 and die 20, as shown in FIG- URE 1, with hard metal washers 40 and 40' disposed between the terminal sealing ring 30 and the ram 18 and between the terminal sealing ring 30 and the die 20, clearly shown in FIGURE 2. The hard metal washers 40 and 40' are preferably made of Kovar and are used to prevent the copper plating on the rings 30 and 30' adjacent the ram and the die from adhering On the The 35 and the emitting surface 34. The ram 18 and die" 20, along with the tube are enclosed in a vaccum envelope (not shown) and vaccum fired between 600 and 700 C.' The vacuum pressure is reduced to 1X10? mm. of mercuryat this temperature. An electricalresistance coil 50 may be used for the vacuum firing proc and above the annealing temperature, and applying presess. The coil 50 is powered by a suitable power supply 52 andcont-rolled by a'variable resistor 54. The tube is processed in astaridardmanner during the vacuum firing.

After vacuum firingand still maintaining a high vacuum, the ram 18'is then forced against the die 20 by a press 56. A pressure of about 25000 p.s.i. on the sealing gasket 38 is applied for 2 to 5 minutes at a temperature of about 500-600 C. The pressure, temperature, time combination can be varied somewhat as long as the tem-' perature is below the melting temperature of copper and above the annealing temperatureythe lower the temperature, the greater the pressure and time requirement-and vice versa. The sealing gasket 38 is extruded under this pressure causingit to adhere to the layers'32 and 32' and a like metal to like metal (copper to copper) seal is made. The spacer washer 42 limits the spacing between the rings 30 and 30'- and also prevents the sealing gasket sure to said rims on both of said sealing rings to compress said sealing gasket causing it'to adhere to said plated surface of said rings. f g

2. A method of pressure sealing two copper plated sealing rings disposedon each of two vacuum envelope sections, said sealingrings being made of a metal substantially harder than said copper plating and protruding outwardly from said envelope sections forming rims, the

method comprising the steps'of placing a spacer ring on a copper plated surface of one of said sealing rings subfrom extruding into the tube and making an electrical short. t 7

Although the seal is a copper-to-copper seal, rings and 30'- made entirely of copper are not practical since a copper will extrude and deform during the pressing operation. This deformation of the copper would destroy the vacuum tight bond with the ceramic. A ring 30 and 30' made of hard metal such as Kovar does not deform in making the ,seal'and therefore retains the vacuum tight bond with theceramic. Further, if copper were used, the

spacer washer 42 would imbed itself in the terminal seal-' ing rings and no longer serve the purpose of fixing the cathode, anode spacing.

FIGURE 3 shows the sealed electron tube. The tube is shown in cross-section in order to illustrate what happens to the copper gasket 38 after pressure is applied. The copper flows, under pressure and is prevented from flowing into the vacuum envelope by the spacer washer.

42. The copper in thus flowing adheres to the adjacent copper plating strips 32 and 32'.

What is claimed is: t

a 1. A method of pressure sealing two vacuum envelope sections, saidsections each having a hard metal sealing ring protruding outwardly from each 'of said sections forming rims, said sealing rings being plated with alsoftg stantially coaxially with said plated surface, said spacer ring being made of a metal: substantially harder than copper, .Placing a copper gasket having a thickness greater than said spacer ring on said copper plated surface of said onetof said sealing rings substantially coaxially with and exterior of said spacer ring, placing'a copper plated surface of the other of said sealing rings on said copper gasket, forming a vacuum of about 1 l0- of mm. of mercury around said sections of said electron'tube,.vacuum firing s'aidtwo sections between about 600 and 700 C., and applying pressure to said rim on both of said sealing rings to compress said copper gasket causing it to adhere to the plated surface of said rings but not 7 deforming said spacer ring.

' the same type as said ductile plating on a plated surface of one of said sealing rings substantially coaxially therewith, placing theplated surface of the other sealing ring adjacent the metal gasket so'that the metal gasket is located intermediate the plated surfaces of the two sealing,

' rings, firing said two sections at a temperature below the melting temperature and abovethe annealing'temperature 1 of said metal gasket and said soft ductile plating, and

plated surface of the other of said sealing rings on said applying pressure tosaid sealing rings to compress said sealing rings together thereby extruding said metal gasket. 4. A method as claimed in claim 3 in which said gasket is copper, said pressure is substantially 25,000 pounds per square inch, and said gasket is heated to a temperature of about 500-600 C. at the, time said pressure is applied.

References (lited by. the Examiner UNITED STATES PATENTS 2,398,449 4/46 Ronei 29-497 2,818,637 1/58 Roberts Q. 29472.5 2,965,962 12/60 Ollendorf et a1. 29470.1

3,024,519 3/62 Leinkram' 317-234 JoHN F. CAMPBELL, Primary Examiner. 

1. A METHOD OF PRESSURE SEALING TWO VACUUM ENVELOPE SECTIONS, SAID SECTIONS EACH HAVING A HARD METAL SEALING RING PROTRUDING OUTWARDLY FROM EACH OF SAID SECTIONS FORMING RIMS, SAID SEALING RINGS BEING PLATED WITH A SOFT DUCTILE METAL, SAID METHOD COMPRISING THE STEPS OF PLACING A HARD METAL SPACER RING ON SAID PLATED SURFACE OF ONE OF SAID SEALING RINGS SUBSTANTIALLY COAXIALLY WITH SAID ONE OF SAID SEALING RINGS, PLACING A SOFT METAL GASKET FABRICATED FROM THE SAME MATERIAL AS SAID SOFT DUCTILE PLATING AND HAVING A THICKNESS GREATER THAN SAID SPACER RING ON A PLATED SURFACE OF SAID ONE OF SAID SEALING RINGS SUBSTANTIALLY COAXIALLY WITH AND EXTERIOR OF SAID SPACER RING, PLACING A PLATED SURFACE OF THE OTHER OF SAID SEALING RINGS ON SAID GASKET SUBSTANTIALLY COAXIALLY WITH SAID SPACER RING, FORMING A VACUUM AROUND SAID SECTIONS, HEATING SAID RINGS AND GASKET TO A TEMPERATURE BELOW THE MELTING TEMPERATURE AND ABOVE THE ANNEALING TEMPERATURE, AND APPLYING PRESSURE TO SAID RIMS ON BOTH OF SAID SEALING RINGS TO COMPRES SAID SEALING GASKET CAUSING IT TO ADHERE TO SAID PLATED SURFACE OF SAID RINGS. 